The present invention relates to lacquer coatings on metal surfaces, especially aircraft bodies or the like.
The outer lacquer coating on an aircraft is normally applied after the final assembly. Conventionally, a so-called wash primer is applied along with a top coating of lacquer or paint. It is also known to use one or several primer coatings between the wash primer and the top coating. Aircrafts are generally repainted after several years, either to improve their appearance or to change their appearance. Heretofore, it was necessary to completely remove the previous paint coat and primer down to the bare metal surface prior to a new paint job. A mere removal of the top coating is not possible in prior art paint and/or lacquer coating. Due to the complete paint removal heretofore required, it is normally unavoidable that the original metal surface treatment is damaged or even completely destroyed, whereby the corrosion protection afforded by the second lacquer coating or paint job is substantially diminished, especially since the so-called filiform-corrosion can be much more effective where the original metal treatment is penetrated or completely removed. Further, it is required that the paint job on modern commercial aircraft is resistant to non-combustible hydraulic fluids. Such hydraulic fluids usually comprise sulphuric acid esters and the so-called wash primer is not resistant or proof against such esters whereby lacquer layers already mechanically damaged may further be damaged due to a creeping action.
The application of a primer which is resistant against sulphuric acid esters on the individual components of the aircraft would have the great advantage that an intimate bonding would be achieved between the primer and the metal surface. This method would also permit the heat treatment of the primer directly on the individual components. In addition, it would be possible to achieve the best metal surface treatment for each individual component whereby a good bond could be achieved between the top coating and the primer. Such good bond in turn would substantially eliminate the so-called filliform-corrosion. Moreover, corrosion due to creeping action at points where sheet metal sections overlap each other or along edges and abutments would be almost completely eliminated. Aircraft manufactured in this manner could be painted with the sulphuric acid ester resistant top coat or lacquer after the final assembly. However, such method of applying the paint coating by priming each individual part separately would prevent the removal of the paint coating, even after several years. Even the use of etching means, such as phenol and cresol containing etching means which are very toxic and hence undesirable from an environmental protection point of view would not be suitable to completely remove such a paint system as described above. Furthermore, the removal by sanding is not only uneconomical, it also destroys the metal surface treatment, such as yellow chromizing or anodizing. Another disadvantage of removing old paint coatings by sanding is seen in that the plating itself could be sanded through.